Email KPIs: Essential Email KPI Metrics to Keep Track Of

Email KPIs: Essential Email KPI Metrics to Keep Track Of

Email marketing is one of the most important marketing channels for most businesses, delivering one of the highest if not the highest ROI, with a reported 4,200% return.

So it’s vital to know how your own email marketing activities are performing. After all, what you can measure, you can grow.

And that means tracking and monitoring a series of email KPIs. In case you’re wondering what KPI stands for, here’s a definition:

KPI = Key Performance Indicator

In other words, each KPI indicates how your business is performing in a specific key area.

To help you do that in relation to email marketing, this post details 7 top email KPI metrics you should be tracking, including how to calculate each one.

But first, a quick warning that doing so is becoming more challenging...

Warning: Apple’s iOS 15 Upset the Apple Cart

Since Apple’s release of Mail Privacy Protection in iOS 15 in September 2021, some of the email KPI metrics below have been rendered less useful than they were before.

That’s because all the people receiving emails in Apple Mail (about 40%) will now show as having opened the email, even though they may not have done so.

Consequently, the number of opens will no longer be accurate.

That means the metric is no longer useful for comparing one business against another.

But it can still be useful within your own business for comparing one email against another (post-iOS 15) because the proportion of people on your list using Apple Mail isn’t going to change much.

So for example from week to week you can see whether a metric like your OR or CTR (see below) has gone up or down, as well as compare metrics for different emails within a particular campaign.

Where Apple’s update impacts the accuracy of a particular email KPI, it’s noted in the relevant section below.

However… having said all of that, some email campaign services are finding workarounds and extrapolating a more accurate open rate (OR).

They do that by simply discounting the opens from Apple Mail, and calculating the OR based on the remaining users.

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Founder, Takanomi

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Top 7 Email KPIs

1. Click-Through Rate (CTR)

Note: this is one of the email KPI metrics affected by Apple’s iOS 15 update referred to above. Use for comparison purposes between emails within your own business only.

This email KPI reflects the proportion of people who have opened your email who went on to click a particular link in it.

In other words, out of everyone who opened your email, it shows you the percentage of people who clicked on a particular link.

If you have more than one link in an email (for example, a newsletter might include several links to different pieces of content), you can compare how each link performed.

Calculating the click-through rate on a per-link basis is also useful for where your emails have, say, links to social profiles, and you want to know the percentage of people who clicked on your specific CTA link(s) rather than any general links.

Note that because of iOS 15, the calculation involves dividing by a higher number of opens than is actually the case, which in turn pushes down the actual percentage you get back.

So in itself it’s not accurate. But it is useful for comparing rates, say week to week, or between links in the same email to see their comparative effectiveness.

For the percentage of people who clicked one or more links in your email, regardless of which one, see CTOR below.

How to Calculate the Click-Through Rate (CTR)

Email KPI metrics: how to calculate the click-through rate, (number of clicks on a specific link / number of emails opened )

2. Click-to-Open Rate (CTOR)

Note: this is one of the email KPI metrics affected by Apple’s iOS 15 update referred to above. Use for comparison purposes between emails within your own business only.

Whereas the CTR metric above is for individual links, this CTOR metric is for your email as a whole.

In other words, it answers the question:

Out of everyone who opened your email, what percentage of people clicked on any link in that email?

The answer tells you the proportion of people who opened your email who actually then went on to click a link in your email.

However, once again since iOS 15, because the number of opens used in the calculation is no longer accurate, the percentage will be artificially lower than it should otherwise be.

As with CTR above, It’s therefore most useful for purposes of comparing results between different emails within your business.

How to Calculate Your Click-to-Open Rate (CTOR)

Email KPIs: how to calculate the click-to-open rate, (number of clicks on any link / number of emails opened) x 100

3. Conversion Rate (CR)

Let’s say you’re sending out an email with a specific goal in mind, such as to sell a particular product as part of a promotion you’re running.

Your conversion rate tells you the percentage of people who took the required action—in this case, purchasing a specific product—out of everyone you sent the email to.

You will need to be able to measure the number of people who specifically converted as a result of your email—such as by clicking on a particular link in the email—rather than everyone else who took the same action.

For example, you may also have ads on Facebook running that advertise the same deal—you don’t want these people included.

How to Calculate the Conversion Rate (CR)

Email KPI metrics: how to calculate the conversion rate, (number of conversions / number of emails sent) x 100

4. Bounce Rate

The bounce rate tells you the percentage of emails that never made it to subscribers’ inboxes.

The reasons include:

  • Permanent issues, such as where the email address doesn’t exist, perhaps as a result of someone leaving a job—this is referred to as a hard bounce...
  • Temporary issues, such as where someone’s inbox is full, or perhaps a server is down—this is referred to as a soft bounce, as future sends to the same email may succeed.

Email addresses that cause hard bounces should be removed from your list.

Some email campaign providers take care of this automatically, ensuring that no further emails will be sent to the person (while keeping the contact itself intact, as there may be other data that’s still valuable such as a physical mailing address).

For soft bounces, these emails are usually kept on your list. Some email campaign providers will:

  • Track the number of soft bounces and treat them as hard bounces after a certain number...
  • Automatically attempt to redeliver the message a certain number of times.

This email KPI is important to keep track of because the metric, if too high, can impact the deliverability of emails to the rest of your list.

It’s generally recommended to keep it less than 2%—if it creeps higher, take action to reduce it by for example:

  • Deleting hard bounce email addresses from your list, or otherwise ensuring delivery won’t be attempted…
  • Doing similar with soft bounce email addresses where the issue remains unresolved after a certain of sends or over a particular time period…
  • Using double opt-in for new leads to avoid corrupted or dummy email addresses that immediately hard bounce.

How to Calculate Your Bounce Rate

Email KPIs: how to calculate the bounce rate, (number of bounces / number of emails sent) x 100

5. Spam Complaint Rate

As with your bounce rate, the number of spam complaints you get affects the deliverability of emails to your list as a whole.

If too many people are reporting your email as spam, it’s a red flag for services like Gmail who are more likely to then send your emails straight to the spam folder for other recipients.

Keep the Spam Complaint Rate email KPI metric as low as possible

While a certain proportion of people will always mark an email as spam even when it’s no such thing, if the number starts to creep up or gets above a certain level, it tells you a few things:

  • Your emails aren’t delivering the kind of value subscribers expected when they first signed up…
  • There’s a mismatch between the tone of your emails, and what subscribers would prefer to receive…
  • You’re not providing an easy way for people to unsubscribe...
  • You might be sending emails to people who haven’t given you the proper permissions to do so.

To fix, reduce the possibility of future spam complaints by doing one or more of the following:

  • Use double opt-in to ensure leads have to confirm that they want to hear from you before receiving messages…
  • Be very clear about how people can unsubscribe—it’s good practice to tell them how to do this in the first email they receive. It’s far better for someone to click an easily accessible unsubscribe link than to mark the email as spam...
  • Ensure people don’t have to jump through hoops after clicking the unsubscribe link to actually leave your list—it should be an easy, virtually instantaneous process...
  • Be clear right from the start about the type of messages you will be sending them…
  • Be consistent in your communications so that the expectations of your leads are set. If you’ve been emailing them once a month, and suddenly switch to once a day, spam complaints are likely to rise simply because it’s not what your leads are used to.

How to Calculate Your Spam Complaints

While you can check spam complaint rates for specific emails, it’s often more useful to measure your spam complaint rate for a specific time period, such as for a month.

The calculation is simple: Email KPI metrics: how to calculate the spam complaint rate, (number of spam complaints / number of emails sent) x 100

6. Open Rate (OR)

Note: this is one of the email KPI metrics affected by Apple’s iOS 15 update referred to above. Use for comparison purposes between emails within your own business only.

Since Apple’s release of iOS 15, the open rate (OR) is no longer accurate.

That’s because anyone on your list who uses Apple Mail (around 40%] will have the email counted as ‘opened’, even when they may not have opened in.

However, the metric is still useful as (at least, once the vast majority of iPhone users are on iOS 15 or later) you’re able to compare one email against another. In other words, it’s a measure of relative performance.

And while there’s an argument that your open rate is largely a vanity metric—after all, email opens don’t necessarily translate into real engagement—it does have an impact on email deliverability.

It’s therefore important to know how your emails perform against each other and work to maximize that performance.

How to Calculate Your Open Rate (OR)

Email KPIs: how to calculate the open rate, (number of emails opened / number of emails sent) x 100

7. List Growth Rate

Of course, you want to know whether your list is growing—or perhaps shrinking—and the rate at which it’s doing so.

You may have a specific KPI you want to hit or exceed each month in relation to the growth of your list to help ensure the continued growth of your business as a whole.

Keeping an eye on this email KPI metric means you can see when your strategies are working, and maybe when you need to ramp things up a bit.

How to Calculate Your List Growth Rate

Email KPI metrics: how to calculate the list growth rate, (net number of new subscribers / total number of subscribers) x 100

To Conclude

So that’s seven top email KPIs to keep track of so you know exactly how your business is performing in key areas related to email marketing.

For each one, I’ve shared exactly how to calculate it.

One way to keep track of them on a regular basis would be to set up a spreadsheet with a tab for each one, and relevant formulae to automate the calculations.

@byStephenDShaw

Stephen D Shaw has ran online businesses for 20 years, including founding the world's first content distribution service that served 1000s of businesses for a decade. He's worked directly with people like Ryan Deiss and Frank Kern, and consulted with a range of 6- to 9-figure businesses.

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